User's Manual

Radio Operation
Crescendo UHF Half-Duplex User Manual Page 25 of 78
9
N/C
Gnd
Gnd
Gnd
10
N/C
Gnd
Gnd
N/C
11
N/C
Gnd
N/C
Gnd
12
N/C
Gnd
N/C
N/C
13
N/C
N/C
Gnd
Gnd
14
N/C
N/C
Gnd
N/C
15
N/C
N/C
N/C
Gnd
16
N/C
N/C
N/C
N/C
Table 11: Channel selection via I/O module
In the table above, “Gnd” indicates that the pin should be connected to ground, and “N/C” means that the pin
should not be connected. Note that channel 16 is selected by default when no pins are connected and “I/O
Selects Channel” is enabled. Also note that the order of the columns in this table matches the layout of pins
on the connector. See Appendix A.3.3 for a pin-out diagram.
In general, channels are numbered starting from 1. However, the Legacy Channel Numbering setting causes
channels to be indexed from 0 when selecting and configuring channels using Hayes commands only. See
Appendix C.4 for details.
5.3.5 Retries
The maximum number of retries per packet can be configured between 0 and 20. When a low number of
retries is selected, the link may become unreliable in the presence of interference or collisions. When a high
number of retries is selected, the link will be more reliable. However, additional retries will induce
substantial latency in the presence of interference.
Two parameters are used to set the number of retries to use:
 Singlecast retries: The number of retries to use on data that is destined for a single receiving radio.
This is applied to any transmission using the point-to-point or Hayes dialup protocols.
If the remote unit is non-existent, due to a misconfigured destination address, the remote being out
of range, or the remote unit being faulty, the data will be retransmitted a number of times equal to
the singlecast retries setting. This can dramatically reduce the throughput of a radio network.
 Broadcast retransmissions: The number of retries to use on data that is destined for multiple
radios. This is applied to any transmission when using the point-to-multipoint protocol, or to any
packet addressed to the broadcast address when using the datagram protocol.
When a unit is broadcasting data, the transmission cannot be acknowledged, as collisions would occur
between the acknowledgements. Instead, a broadcasting unit will transmit all data a fixed number of times
equal to the broadcast retransmissions parameter, and receiving units will discard any duplicate data
received.
Two parameters determine how long the Crescendo will wait for an acknowledgement after transmission
before retrying. These parameters are:
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